Understanding the complex surface and solution behaviour of di-alkyl chain cationic and nonionic surfactant mixtures is important for a wide range of applications including detergents, shampoos, and conditioners. Furthermore, by analogy, it has wider implications for membrane solubilisation, a key technique in biochemistry, and for the manipulation of membrane properties.

Neutron reflectivity, small angle neutron scattering, light scattering, and surface tension have been used to characterize surface and solution behaviours of the cationic surfactant, di-hexedecyl dimethyl ammonium bromide, DHDAB, with a range of different nonionic surfactants, from C₁₂E₃ to C₁₂E₁₂.

Solution phase behaviour for the different cationic / nonionic mixtures has been determined in some detail. For the nonionic surfactants C₁₂E₆ and C₁₂E₁₂ the nonionic rich region of the phase diagram is comprised of mixed globular micelles. For the cationic rich composition the predominant microstructures are bi-lamellar to multi-lamellar vesicles and L_β lamellar phase. At intermediate compositions there is a coexistence region comprised of micellar and planar structures in coexistence. For C₁₂E₃ the phase behaviour is different and shows an evolution of different planar structures with composition.

The surface behaviour is characterized by a much more marked departure form ideal mixing than is normally encountered in surfactant mixtures. For solutions rich in cationic the surface adsorption is dominated by the cationic surfactant, and the nonionic only competes for the surface for solutions rich in the nonionic surfactant. It is shown how this surface behaviour is correlated with the solution phase behaviour which is determining the relative monomer composition and concentrations.